ALAMEDA, Calif. -- Just when quarterback Aaron Brooks returned to give Oakland's struggling offense a needed boost, the Raiders lost starting running back LaMont Jordan to a knee injury that could sideline him for the rest of the season.

Jordan underwent an MRI on Monday, a day after tearing the medial collateral ligament in his left knee. Coach Art Shell didn't know the extent of the tear when he addressed the media and was unsure how long Jordan would be sidelined.

Jordan said he wouldn't need surgery on the knee, but wouldn't speculate how long he would be out. But with only six games remaining this season and the Raiders out of contention, it's unlikely he'd be able to make it back.